ElasticSearch S3 repository Snapshot to Spaces fails

I have installed ElasticSearch 6.2 on a droplet running ubuntu 16.04 and what to create a s3 repository that backup my ElasticSearch database to a space though the S3 Spaces API. For some reason, I keep getting the same error every time, I try to create my repository:

{"error":{
     "root_cause":[{
          "type":"blob_store_exception",
          "reason":"Failed to check if blob [master.dat-temp] exists"}],
     "type":"blob_store_exception",
     "reason":"Failed to check if blob [master.dat-temp] exists",
     "caused_by":{
          "type":"amazon_s3_exception",
          "reason":"Forbidden (
               Service: Amazon S3;
               Status Code: 403;
               Error Code: 403 Forbidden;
               Request ID: THEREQUESTID;
               S3 Extended Request ID: THEEXTENDEDREQUESTID)"}},
"status":500}

I might add, that I also have a droplet running with ElasticSearch 5.6 and on that droplet, there is no problem creating s3 repositories and backing up my data to Spaces.

What I’m I missing?